The present invention relates to methods of employing a range adaptable system for determining the angular position and distance of a radiating point source as well as the system itself. In the present invention, radiation from a point source travels through a window mask pattern and onto the surface of a sensor. In the prior art, this general concept is well known, however, the prior art fails to teach or suggest the specific techniques employed by Applicant to accurately measure angular position and distance using such a structure.
Prior art systems have used masked or coded apertures placed above multi-element detectors. All of these techniques have attempted to determine the position of a projected pattern on a detector surface by comparing signals from fixed detector elements arranged in a unique pattern or from comparison to fixed reference signals previously stored in a computer. Such techniques result in limited resolution due to the fact that the magnified mask projection due to point source illumination does not precisely correlate or match the fixed detector pattern or reference signal.
As an example of the effect of magnification on the alignment process, resolving patterns with as many as 100 line/space pairs, there must be less than one part in 400 magnification in order to preserve correlation with a fixed reference. This level of magnification may typically occur at a distance of between 2 and 4 meters (6 to 13 feet), which represents the outer range of most optical position measurement systems. In order to facilitate operation at closer distances, with high resolution performance, a means of scale identification is required. It is with this notion in mind, among others, that the present invention was developed.
The following prior art is known to Applicant:
U.S. Pat. Nos. 4,193,689 and 4,314,761, both to Reymond et al. disclose arrangements for locating radiating point sources including the use of a single axis detector array and an aperture mask containing a slit to project light onto the array. In the earlier patent, a cylinder lens is used, and in the later patent, the cylinder lens is replaced with an aperture that can be shuttered to allow light in from preferred directions. In each case, three single axis arrays are used, and three cameras are required to compute three planes that intersect to define a point in space. The embodiments of the present invention differ from the teachings of the Reymond et al. patents since they include computing means to determine scales and shifts of image components and wherein the mask is not a single slit.
U.S. Pat. No. 4,209,780 to Fenimore et al. and U.S. Pat. No. 4,389,633 to Fenimore disclose the technique of using uniformly redundant arrays for coded aperture imaging. Correlation between mask and image is used to determine a lag function of the received mask pattern. A mosaic pattern is disclosed as yielding results superior to those yielded through the use of a random array. In the Fenimore '633 patent, the mask and detector are either one or two dimensional. The Fenimore '780 patent only discloses two dimensional imaging. The present invention differs from the teachings of the Fenimore patents since it does not compare image to a fixed reference pattern.
U.S. Pat. No. 4,435,838 to Gourlay discloses the concept of imaging planes of various distances in the field of tomographic imaging. The Gourlay technique improves the prior art process of selecting various image sizes to correlate with detector response to select a particular depth plane. Gourlay teaches the setting of a coded aperture at a distance D/d, where D is the object-to-detector distance and d is the object-to-mask distance, so that the image can be kept at the same magnification, thereby simplifying the correlation process. The present invention differs from both that of Gourlay and that of prior art systems in the field of tomographic imaging, since, in the present invention, various object-to-mask distances or various image sizes are not chosen to select a particular depth, but, instead, the mask image scale is automatically determined using frequency domain techniques.
Applicant is also aware of U.S. Pat. Nos. 5,408,323 to Mitchelson and 6,141,104 to Schulz. Each of these references teaches the concept of the use of a random pattern mask or universal redundant array. In each of these patents, measurement is conducted by comparing actual measurements to previously stored reference measurements. Over and above the reasons why the present invention, in its embodiments, patentably distinguishes from the Reymond et al. patents, the present invention distinguishes from Fenimore, Mitchelson, Gourlay and Schulz as specifically avoiding comparison of actual measurements to reference measurements.